Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the workpiece (substrate) deposition surface, a plating layer, e.g.,  of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon-based material having good mechanical (i.e., tribological) properties. A similar situation exists with MO media, wherein a layer stack is formed which comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
According to conventional manufacturing methodology, a majority of the above-described layers constituting magnetic and/or MO recording media are deposited by cathode sputtering, typically by means of multi-cathode and/or multi-chamber sputtering apparatus wherein a separate cathode comprising a selected target material is provided for deposition of each component layer of the stack and the sputtering conditions are optimized for the particular component layer to be deposited. A plurality of cathodes each comprised of a selected target material for a particular layer can be positioned within a single or in respective process sub-chambers located within a larger chamber, or a single cathode may be provided in each of a plurality of separate, interconnected process chambers each dedicated for deposition of a particular layer. According to such conventional manufacturing technology, a plurality of media substrates, typically in disk form, are serially transported by means of a multi-apertured pallet or similar type holder, in linear or circular fashion, depending upon the physical configuration of the particular apparatus utilized, from one sputtering target and/or process chamber to another for sputter deposition of a selected layer thereon.
Cost-effective productivity requirements imposed by automated manufacturing technology for magnetic and MO media require maximized sputter deposition rates, while at the same time, high quality, high areal recording density media require high purity thin film layers which exhibit respective  physical, chemical, and/or mechanical properties, including, inter alia, proper crystal morphology necessary for obtaining high areal recording densities, e.g., polycrystallinity; good magnetic properties, e.g., coercivity and squareness ratio; chemical stability, e.g., inertness or corrosion resistance; and good tribological properties, e.g., wear resistance and low stiction/friction. Frequently (but not necessarily), obtaining such desirable physical, chemical, and/or mechanical properties for each of the constituent layers of the multi-layer media requires application of an electrical bias potential to the substrate during sputtering, e.g., a DC, AC, or RF bias potential, or some combination thereof, wherein the bias type and level of bias potential is optimized for each constituent layer. For example, application of a suitable substrate bias during sputter deposition of metal-based underlayers and ferromagnetic metal alloy layers of thin film magnetic recording media can facilitate formation of preferred crystal orientations, and increase carbon (C) density of C-based protective overcoat layers of thin film magnetic and MO recording media.
Currently, application of optimum substrate bias to disk substrates for deposition thereon of particular films or layers poses no problem when processing is performed on a single-disk basis in separate chambers dedicated for deposition of the particular layers, e.g., as with the Intevac 250B and Unaxis M14 systems. However, when the films or layers are deposited in a more cost-effective manner at high product throughput onto closely-packed pluralities of disk substrates carried by a moving pallet, i.e., an elongated, electrically conductive pallet, application of optimum substrate bias for particular film or layer deposition thereon may be problematic. For example, and particularly where a plurality of different coating material sources, e.g., magnetron sputtering sources, are located in spaced adjacency within a single vacuum chamber of an in-line apparatus, application of different bias potentials to the moving pallet as the disks carried thereon pass by a particular cathode may be difficult, if not impossible, for the following reason: in such in-line apparatus, sliding electrical bias contactors are  located on a single potential rail that contacts the bottom edge of the pallet as it passes through the chamber, maintaining the pallet at that bias potential for as long as the pallet remains in the process chamber. A different bias potential may be applied to the pallet via a second rail only when the pallet is able to move across a space not provided with a potential rail, provided the non-rail space has a length equal to or greater than the length of the pallet.
According to one approach for application of optimal bias potentials in in-line, multi-cathode systems, adjacent cathodes for sputter deposition of different constituent layers of magnetic and/or magneto-optical (MO) recording media, e.g., the Cr cathode for deposition of the polycrystalline underlayer and the cathode for deposition of the magnetic recording layer, are spaced apart a pallet-length (more specifically, a standard chamber-length) in order to allow for application of separate bias potentials for each of the layers. However, such approach disadvantageously requires long chamber lengths, increased pumping capacity and system footprint or area, as well as substantially increased cost. Moreover, recent improvements in recording media design have necessitated an increase in the number of thin film layers to be deposited as part of the multi-layer stack, and as a consequence, additional cathodes have been installed in the chamber, e.g., between the previously well-spaced cathodes for Cr and magnetic recording layer deposition, in turn necessitating deposition of all of the films or layers at the same substrate bias potential. For example, typical recent media designs require deposition of 7–9 distinct layers, and future superlattice-based media will require as many as 50 separate layers. In either instance, separation of adjacent cathodes by a pallet length to provide optimum bias potentials is clearly impractical in terms of cost and system size, and the alternative of continuing to process pallets at less than optimum bias potentials is similarly unattractive, in that the attendant loss of media performance may be as high as several dB in SMNR. 
Accordingly, there exists a need for improved means and methodology for forming, as by plasma treatment or physical vapor deposition techniques, e.g., sputtering, under optimal substrate bias potentials and at processing rates consistent with the throughput requirements of automated manufacturing processing, multi-layer thin film stacks and laminates on the surfaces of a plurality of substrates carried by a common pallet, which means and methodology overcomes the above-described drawbacks associated with the difficulty in applying a desired, i.e., optimal, substrate bias during deposition of each constituent layer of the stack. More specifically, there exists a need for improved means and methodology for bias sputtering high purity, high quality, thin film layer stacks or laminates having optimal physical, chemical, and/or mechanical properties for use in the manufacture of single- and/or dual-sided magnetic and/or MO media, e.g., in the form of disks, which means and methodology provide rapid simple, and cost-effective formation of such media, as well as various other products and manufactures comprising a stack or laminate of thin film layers.
In particular, the present invention addresses and solves problems attendant upon performing bias sputter deposition of a plurality of thin film layers onto optimally electrically biased workpieces, which thin film deposition is utilized, inter alia, in the manufacture of high quality, thin film magnetic and/or magneto-optical (MO) recording media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology therefor. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of various devices and articles requiring high purity, high quality thin films with optimal physical, chemical, and/or mechanical properties. 